1. Field of the Invention
This invention relates to an improved process for preparing vinylic pentavalent organophosphorus compounds. More particularly, this invention relates to a process of preparing vinylic pentavalent organophosphorus diester compounds from the corresponding allylic pentavalent organophosphorus diester compound by alkali metal hydroxide induced isomerization.
2. Prior Art
Esters of vinyl phosphonic acid serve as useful reactants in a large number of reactions to form compounds which are useful in agriculture. The versatility of this intermediate material results from reactivity of the vinylic group toward nucleophilic compounds. By manipulations of this reactivity via reaction with nucleophilic compounds such as alcohols, thiols, amines, nitroalkanes, active methylene compounds and the like, a wide class of agricultural chemicals can be prepared. For example, esters of vinylphosphonic acid compounds can be reacted with phosgene or oxalyl chloride to prepare plant growth regulants as described in detail in German Offen No. 2,153,149 (1973). Similarly, such esters can be reacted with amines to accordance with the procedures described in Bartlett et al., Tet letters, 24:2937 (1983) to prepare phosphatase inhibitors.
Furthermore, esters of vinyl-phosphonic acid can be used as precursors in the preparation of compounds which can be used in fields other than agriculture. For example, these compounds can be used in the preparation of heat and light stabilizers for polymers as well as flame retardant or shrinkage retardant additives for polymers. Such uses are described in detail in U.S. Pat. Nos. 4,129,710, 2,784,206 and 2,784,169; Ger. Offen 2,745,982; J. Appl. Polym. Sci. 22:2403-14 (1978); J. Org. Chem (USSR) 19:1789 (1983) and the like.
Heretofore some synthetic procedures for the preparation of vinylic phosphonate compounds have centered on reacting an appropriate vinylic halide with an appropriate trivalent phosphorous esters in accordance with the following reaction scheme: ##STR1## This procedure is known as the Michaeles-Arbuzov reaction. Examples of this procedure are described in "Organic Phosphorous Compounds", Vol. 7 pgs. 1-486, John Wiley & Sons (1976). The Michaeles-Arbuzov reaction suffers from a number of well-known inherent defects. For example, except for the .alpha.,.beta.-unsaturated systems, reactions involving the Michaeles-Arbuzov reaction have failed.
Similarly reactions involving the use of transition metal salt catalyst have been used to prepare vinylic phosphonate compounds. For example, the transition metal salt catalyzed reaction of aromatic and vinylic halides with phosphites or similar trivalent phosphorus compounds to prepare the corresponding vinylic phosphonate compound is described in U.S. Pat. No. 3,493,639. This procedure also suffers from a number of inherent defects. For example, severe reaction conditions have limited the application of this procedure in industrial applications.
It is thus apparent that a need exists for an improved, practical and efficient method for the preparation of vinyl phosphonate esters.